prg13_4shmwr.c

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#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <sys/mman.h>

#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
int main(int argc,char **argv)
{
  int  c,fd,flags;
  unsigned char  *ptr,*rptr;
  off_t  length;
  struct stat wstat;
  flags = O_RDWR | O_CREAT;
  int i;
  if (argc != 3)
  {
  	printf("usage %s: <name> <length>",argv[0]);
  	exit(0);
  }
  
  while((c = getopt(argc,argv,"e")) !=-1)
  {
  	switch(c)
  	{
  		case 'e':
  			flags |= O_EXCL;
  			break;
  	}
  }
  
  length = atoi(argv[2]);
  fd = shm_open(argv[1],flags,FILE_MODE);
  ftruncate(fd,length);
  fstat(fd,&wstat);  //获取大小信息
  ptr = mmap(NULL,length,PROT_READ | PROT_WRITE,MAP_SHARED,fd,0);
  close(fd);
  
  if (wstat.st_size > 0)
    printf("already created and now writing\n"); 
  for(i=0;i<wstat.st_size;i++)
  {
    *ptr++ = i%256;
    printf("%d",*(ptr-1));
  }
  printf("\n");

  fd = shm_open(argv[1],O_RDONLY,FILE_MODE);
  fstat(fd,&wstat);
  rptr = mmap(NULL,wstat.st_size,PROT_READ,MAP_SHARED,fd,0);
  close(fd);

  if (wstat.st_size >0)
    printf("now reading\n");
  for(i=0; i<wstat.st_size;i++)
  {
    if ((c=*rptr++) != (i % 256))
      printf("not equal rptr[%d] = %d",i,c);
    else
      printf("%d",c);
  }
  printf("\n");
  
  shm_unlink(argv[1]);
  exit(0);
}